Linda Poon is a staff writer at CityLab covering science and urban technology, including smart cities and climate change. She previously covered global health and development for NPR’s Goats and Soda blog.
An “unprecedented” hurricane may bring three dangerous kinds of flooding all at once: rainfall, a storm surge, and overflow from a swollen Mississippi River.
As Hurricane Barry barrels toward the Louisiana coast, New Orleans is already soaked and facing the prospect of “unprecedented” flooding in the coming days.
Thunderstorms drenched the Gulf Coast on Wednesday, leaving parts of the city with as much as eight inches of rain. Some areas are still under water and some residents are without power as they prepare for the next big storm. Hurricane Barry is expected to hit land on Saturday about 85 miles west of New Orleans, bringing nearly two more feet of rain and winds up to 57 miles per hour.
The National Weather Service says the Mississippi River already surged to 16.5 feet on Friday morning, and could hit 19 feet once the hurricane arrives. That puts the water level dangerously close to exceeding the city’s 20-foot levees.
As the storm approaches, photos from the threatened area paint a harrowing image as residents brace for the worst.
The storm, experts warn, will likely be “unprecedented” in that it will cause three kinds of flooding at once: overflow of the Mississippi River, storm surge from the Gulf of Mexico, and heavy rainfall. In fact, what worries officials and experts most is not the storm surge, but the rain. “Heavy rain is the No. 1 threat,” a local meteorologist with the National Weather Service told the Wall Street Journal. “This could be torrential rainfall: heavy rainfall in quick, quick bursts.”
After Wednesday’s storm, Louisiana Governor John Bel Edwards declared a state of emergency. Search and rescue teams have been deployed, along with 3,000 members of the National Guard. Local officials have ordered mandatory evacuations for residents in low-lying areas.
New Orleans Mayor LaToya Cantrell, meanwhile, is asking residents to shelter in place. Residents who are staying in their homes are trying to protect their homes and businesses with sandbags, and stocking up on food, drinking water, and emergency supplies.
This kind of flooding is unprecedented now, but could become the norm in the future. As CityLab has reported, for every 1 degree Fahrenheit increase in temperatures, the atmosphere holds about 4 percent more water vapor. That puts cities in hot, humid, and coastal areas at particular risk. Morgan City, located 70 miles west of New Orleans, is one such place. Residents there have managed to escape major hurricanes for the last 10 years, but this time, they find themselves right where Barry is expected to make landfall.
The city has a drainage pumping system that can remove the first five inches of stormwater, according to the New York Times. After that, the pumps can only handle about one inch per hour.
“If it comes in a band,” Mayor Frank Grizzaffi told the paper, “our pumps play a catch-up game.”